1. Field of the Invention
This invention relates to mechanism for generating electronically a call signal transmitted by a master unit of an intercom, i.e. an intercommunication system, to several remote units of such system and utilizing such transmitted signal to produce an audible call or alerting signal at only a selected one of the remote units.
2. Prior Art
It is recognized that intercommunication systems have previously used the conventional electrical power wiring in a building for electrically connecting different units of the system for electric transmission of conversations. Such intercommunication systems have included a master unit and several remote units. Also intercommunication systems having wiring separate from the power wiring have included a call signal arrangement by which a call or alerting signal could be sent from the master unit to any one of a number of remote units, but in such systems separate call buttons have been provided at the master unit directly wired, respectively, to the several remote units. Such a system is disclosed in Blivice et al. U.S. Pat. No. 3,404,393, for example. It is understood, however, that in previous intercoms incorporating a master unit and several remote units utilizing the power wiring in a building there has not been a single call signal actuator at the master unit which could be operated to transmit a call signal to only one remote unit selected from several or from a considerable number of remote units without the necessity of having a call circuit from the master unit to each particular remote unit.